Node net socket.end event fires twice? - node.js

Question

This event is firing twice. I'm trying to figure out why.
On one client, I have:
import Net from 'net';
import Chalk from 'chalk';
const fallback = [2,5,10,25,50,100,250,500,1000,2000];
class LocalNetworkInterface {
constructor({path}) {
this._sock = new Net.Socket();
this._pending = {};
this._count = 0;
this._retry = 0;
const connect = () => {
this._sock.connect({path});
};
this._sock.on('connect',() => {
this._retry = 0;
console.log(`Connected to ${Chalk.underline(path)}`);
});
this._sock.on('data',buffer => {
let data = JSON.parse(buffer);
this._pending[data.queryId].resolve(data);
delete this._pending[data.queryId];
});
this._sock.on('end', () => {
console.log(`Lost connection to ${Chalk.underline(path)}. Attempting to reconnect...`);
connect();
});
this._sock.on('error', err => {
if(err.code === 'ENOENT') {
let ms = fallback[this._retry];
if(this._retry < fallback.length - 1) ++this._retry;
console.log(`Socket server unavailable. Trying again in ${ms}ms`);
setTimeout(connect, ms);
}
});
connect();
}
// ...
}
And the server:
const sockServer = Net.createServer(c => {
c.on('data', buffer => {
let data = JSON.parse(buffer);
// log('Received',data);
let ql = queryLogger();
runQuery(Object.assign({}, data, {schema})).then(result => {
ql(`${Chalk.magenta('socket')} ${print(data.query).trim()}`);
let response = Object.assign({}, result, {queryId: data.queryId});
c.write(JSON.stringify(response));
});
})
});
sockServer.on('error', serverError => {
if(serverError.code === 'EADDRINUSE') {
let clientSocket = new Net.Socket();
clientSocket.on('error', clientError => {
if(clientError.code === 'ECONNREFUSED') {
FileSystem.unlink(SOCK_FILE, unlinkErr => {
if(unlinkErr) throw unlinkErr;
sockServer.listen(SOCK_FILE, () => {
log(`Sock server improperly shut down. Listening on '${sockServer.address()}'`)
});
});
}
});
clientSocket.connect({path: SOCK_FILE}, () => {
throw new Error(`Server already running`);
});
}
});
['SIGTERM','SIGINT'].forEach(signal => process.on(signal, () => {
console.log(`\rReceived ${Chalk.yellow(signal)}, shutting down ${Chalk.red('❤')}`);
sockServer.close();
process.exit();
}));
sockServer.listen(SOCK_FILE, () => {
log(`Listening on ${Chalk.underline(sockServer.address())}`)
});
When I restart the server, I see "Lost connection" twice on the client. Why?
The documentation says:
Emitted when the other end of the socket sends a FIN packet.
The server isn't sending two "FIN" packets is it? Any way I can verify?

Answer 1

Seeing this in docs in regard to connect...
"...This function is asynchronous. When the 'connect' event is emitted the socket is established. If there is a problem connecting, the 'connect' event will not be emitted, the 'error' event will be emitted with the exception."
The fact that the connect event might simply not be firing simply making it look to you like the end event fired twice? Like #robertklep said, maybe expand that error check for more than specific code.

Answer 2

I think it's because on end, I immediately try to reconnect and then the same event is being caught again. Seems kind of strange that it would do that, but delaying it to the next tick works:
this._sock.on('end', () => {
console.log(`${Chalk.yellow('Lost connection')} to ${Chalk.underline(path)}. Attempting to reconnect...`);
process.nextTick(connect);
});